Woody said there are no definite or clear-cut motives for the attacks, but pointed out that bus drivers often have to deal with problems on their own and unarmed.

"Any situation that flares up on the bus, these drivers have to handle on their own and it leaves them open for retaliation," he said. "You know exactly when and where they're' going to be so it would be very easy to retaliate against them. These types of crimes are crimes of opportunity, crimes of randomness that have no real recordable value to them."

ATU's Hanley said "absolutely not enough" is currently being done in the U.S. and in Canada to protect drivers, but efforts are underway.

They are fighting to put cameras in all buses, to increase police presence, install protective shields and implement more safety training for drivers.

Though the shields can be put in buses after manufacturing, Hanley said most buses are not currently engineered for them so a driver's already cramped work stations can become claustrophobic and have ventilation problems.

Long-term solutions include new buses pre-engineered for the shields and doors on the driver's side.

"You wouldn't want to buy a car with no driver's door," Hanley said. "Think about yourself being cramped in the work station that drivers have with your back to two walls, a steering wheel in front of you and someone standing over you beating you."

"[There's] one way out and it's through the person beating your brains in," he said. "At least if the drivers could escape, we would have people with less serious injuries."